1. Field of the Invention
This invention relates to a nonaqueous electrolyte secondary battery.
2. Description of the Related Art
In recent years, with a view to meeting the demand to further miniaturize and saving weight in electronic equipment such as mobile telecommunication equipment, notebook personal computers, a handheld personal computers, integrated video cameras, portable CD (MD) players, a cellular telephones, etc., there is an increasing demand to develop, as a power source for this electronic equipment, a battery which is especially small in size and very large in capacity.
As for the batteries which are now extensively employed as a power source of this electronic equipment, typical examples thereof include a primary battery such as an alkali-manganese battery, and a secondary battery such as a nickel-cadmium battery and a lead storage battery. Among these batteries, a nonaqueous electrolyte secondary battery where the positive electrode thereof contains a lithium composite oxide and the negative electrode thereof contains a carbonaceous material which is capable of intercalating and releasing lithium ions is now attracting much attention because of the fact that it is possible, with the employment of this nonaqueous electrolyte secondary battery, to realize the miniaturization and weight reduction of the battery, and to enhance the cell voltage as well as energy density.
As for active materials for the positive electrode of the nonaqueous electrolyte secondary battery, it is proposed in Japanese Laid-open Patent Publication (Kokai) No. 10-69910 (1998) to employ lithium nickel composite oxide represented by a general formula (1) of Liv-x1Ni1-x2MxO2, features being that a diffraction peak ratio at (003) plane and (104) plane, i.e. (003)/(104), in terms of Miller indices “hkl” of X-ray diffraction, is not less than 1.2, that an average particle diameter “D” falls within the range of 5 to 100 μm, and that the particle size distribution is such that 10% thereof is 0.5 D or more and 90% thereof is 2 D or less.
However, the secondary battery comprising a positive electrode containing this kind of lithium nickel composite oxide is accompanied with a problem that since an oxidative decomposition reaction is permitted to take place in the nonaqueous electrolyte, the charge/discharge cycle life of the battery is relatively short.